Move sse opts into contrib/intel

Makefile.am

@@ -83,11 +83,6 @@ libpng@PNGLIB_MAJOR@@PNGLIB_MINOR@_la_SOURCES += arm/arm_init.c\
 	arm/filter_neon.S arm/filter_neon_intrinsics.c
 endif
 
-if PNG_INTEL_SSE
-libpng@PNGLIB_MAJOR@@PNGLIB_MINOR@_la_SOURCES += intel/intel_init.c\
-    intel/filter_sse2_intrinsics.c
-endif
-
 nodist_libpng@PNGLIB_MAJOR@@PNGLIB_MINOR@_la_SOURCES = pnglibconf.h
 
 libpng@PNGLIB_MAJOR@@PNGLIB_MINOR@_la_LDFLAGS = -no-undefined -export-dynamic \

configure.ac

@@ -314,41 +314,6 @@ AM_CONDITIONAL([PNG_ARM_NEON],
       *)    test "$enable_arm_neon" != '';;
     esac])
 
-# INTEL
-# ===
-#
-# INTEL SSE (SIMD) support.
-
-AC_ARG_ENABLE([intel-sse],
-   AS_HELP_STRING([[[--enable-intel-sse]]],
-      [Enable Intel SSE optimizations: =no/off, yes/on:]
-      [no/off: disable the optimizations;]
-      [yes/on: enable the optimizations.]
-      [If not specified: determined by the compiler.]),
-   [case "$enableval" in
-      no|off)
-         # disable the default enabling:
-         AC_DEFINE([PNG_INTEL_SSE_OPT], [0],
-                   [Disable Intel SSE optimizations])
-         # Prevent inclusion of the assembler files below:
-         enable_intel_sse=no;;
-      yes|on)
-         AC_DEFINE([PNG_INTEL_SSE_OPT], [1],
-                   [Enable Intel SSE optimizations]);;
-      *)
-         AC_MSG_ERROR([--enable-intel-sse=${enable_intel_sse}: invalid value])
-   esac])
-
-# Add Intel specific files to all builds where the host_cpu is Intel ('x86*')
-# or where Intel optimizations were explicitly requested (this allows a
-# fallback if a future host CPU does not match 'x86*')
-AM_CONDITIONAL([PNG_INTEL_SSE],
-   [test "$enable_intel_sse" != 'no' &&
-    case "$host_cpu" in
-      i?86|x86_64) :;;
-      *)    test "$enable_intel_sse" != '';;
-    esac])
-
 AC_MSG_NOTICE([[Extra options for compiler: $PNG_COPTS]])
 
 # Config files, substituting as above

contrib/intel/Makefile.am.patch

@@ -0,0 +1,17 @@
+
+#
+# Copyright (c) 2016 Google, Inc.
+#
+# This code is released under the libpng license.
+# For conditions of distribution and use, see the disclaimer
+# and license in png.h
+#
+
+# In order to compile Intel SSE optimizations for libpng, please add
+# the following code to Makefile.am directly beneath the
+# "if PNG_ARM_NEON ... endif" statement.
+
+if PNG_INTEL_SSE
+libpng@PNGLIB_MAJOR@@PNGLIB_MINOR@_la_SOURCES += intel/intel_init.c\
+    intel/filter_sse2_intrinsics.c
+endif

contrib/intel/configure.ac.patch

@@ -0,0 +1,46 @@
+#
+# Copyright (c) 2016 Google, Inc.
+#
+# This code is released under the libpng license.
+# For conditions of distribution and use, see the disclaimer
+# and license in png.h
+#
+
+# In order to compile Intel SSE optimizations for libpng, please add
+# the following code to configure.ac under HOST SPECIFIC OPTIONS
+# directly beneath the section for ARM.
+
+# INTEL
+# ===
+#
+# INTEL SSE (SIMD) support.
+
+AC_ARG_ENABLE([intel-sse],
+   AS_HELP_STRING([[[--enable-intel-sse]]],
+      [Enable Intel SSE optimizations: =no/off, yes/on:]
+      [no/off: disable the optimizations;]
+      [yes/on: enable the optimizations.]
+      [If not specified: determined by the compiler.]),
+   [case "$enableval" in
+      no|off)
+         # disable the default enabling:
+         AC_DEFINE([PNG_INTEL_SSE_OPT], [0],
+                   [Disable Intel SSE optimizations])
+         # Prevent inclusion of the assembler files below:
+         enable_intel_sse=no;;
+      yes|on)
+         AC_DEFINE([PNG_INTEL_SSE_OPT], [1],
+                   [Enable Intel SSE optimizations]);;
+      *)
+         AC_MSG_ERROR([--enable-intel-sse=${enable_intel_sse}: invalid value])
+   esac])
+
+# Add Intel specific files to all builds where the host_cpu is Intel ('x86*')
+# or where Intel optimizations were explicitly requested (this allows a
+# fallback if a future host CPU does not match 'x86*')
+AM_CONDITIONAL([PNG_INTEL_SSE],
+   [test "$enable_intel_sse" != 'no' &&
+    case "$host_cpu" in
+      i?86|x86_64) :;;
+      *)    test "$enable_intel_sse" != '';;
+    esac])

pngpriv.h

@@ -183,12 +183,18 @@
 #endif /* PNG_ARM_NEON_OPT > 0 */
 
 #ifndef PNG_INTEL_SSE_OPT
+#   ifdef PNG_INTEL_SSE
+      /* Only check for SSE if the build configuration has been modified to
+       * enable SSE optimizations.  This means that these optimizations will
+       * be off by default.  See contrib/intel for more details.
+       */
 #     if defined(__SSE4_1__) || defined(__AVX__) || defined(__SSSE3__) || \
        defined(__SSE2__) || defined(_M_X64) || defined(_M_AMD64) || \
        (defined(_M_IX86_FP) && _M_IX86_FP >= 2)
 #         define PNG_INTEL_SSE_OPT 1
 #      endif
 #   endif
+#endif
 
 #if PNG_INTEL_SSE_OPT > 0
 #   ifndef PNG_INTEL_SSE_IMPLEMENTATION